Extreme ultraviolet lithography method, extreme ultraviolet mask and formation method thereof

ABSTRACT

A method of forming an extreme ultraviolet (EUV) mask includes forming a multilayer Mo/Si stack comprising alternating stacked Mo and Si layers over a mask substrate; forming a ruthenium capping layer over the multilayer Mo/Si stack; doping the ruthenium capping layer with a halogen element, a pentavalent element, a hexavalent element or combinations thereof; forming an absorber layer over the ruthenium capping layer; and etching the absorber layer to form a pattern in the absorber layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is divisional application of U.S. application Ser. No.16/900,384, filed Jun. 12, 2020, which is herein incorporated byreference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advancements to berealized, similar developments in IC processing and manufacturing areneeded.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying Figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic view of an EUV lithography tool with an LPP-basedEUV radiation source, in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a simplified schematic diagram of a detail of an extremeultraviolet lithography tool according to an embodiment of thedisclosure showing the exposure of photoresist coated substrate with apatterned beam of EUV light.

FIGS. 3A, 3B, 3C and 3D are cross-sectional views of various stages of aprocess for forming an extreme ultraviolet (EUV) mask in accordance withsome embodiments.

FIG. 4A is a cross-sectional view of the extreme ultraviolet (EUV) maskunder exposure of the EUV radiation in accordance with some embodiments.

FIG. 4B is a diagram illustrating a mechanism of hydrocarbon from agaseous organic compound deposition on the EUV mask.

FIGS. 5A, 5B, and 5C are cross-sectional views of various stages of aprocess for forming an extreme ultraviolet (EUV) mask in accordance withsome embodiments.

FIG. 6 is a cross-sectional view of various stages of a process forforming an extreme ultraviolet (EUV) mask in accordance with someembodiments.

FIG. 7A shows a flowchart illustrating a method of manufacturing an EUVmask for a semiconductor manufacturing operation according to anembodiment of the present disclosure.

FIG. 7B shows a flowchart illustrating a method of manufacturing an EUVmask for a semiconductor manufacturing operation according to anembodiment of the present disclosure.

FIG. 7C shows a flowchart illustrating a method of manufacturing an EUVmask for a semiconductor manufacturing operation according to anembodiment of the present disclosure.

FIG. 8 shows a flowchart illustrating a method of extreme ultravioletlithography (EUVL) according to an embodiment of the present disclosure.

FIGS. 9A and 9B show a photo mask data generating apparatus according toan embodiment of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the Figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe Figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

To address the trend of the Moore's law for decreasing size of chipcomponents and the demand of higher computing power chips for mobileelectronic devices such as smart phones with computer functions,multi-tasking capabilities, or even with workstation power. Smallerwavelength photolithography exposure systems are desirable. Extremeultraviolet (EUV) photolithography technique uses an EUV radiationsource to emit an EUV light ray with wavelength of about 13.5 nm.Because this wavelength is also in the x-ray radiation wavelengthregion, the EUV radiation source is also called a soft x-ray radiationsource. The EUV light rays emitted from a laser-produced plasma (LPP)are collected by a collector mirror and reflected toward a patternedmask.

FIG. 1 is a schematic view of an EUV lithography tool with an LPP-basedEUV radiation source, in accordance with some embodiments of the presentdisclosure. The EUV lithography system includes an EUV radiation source100 to generate EUV radiation, an exposure device 200, such as ascanner, and an excitation laser source 300. As shown in FIG. 1, in someembodiments, the EUV radiation source 100 and the exposure device 200are installed on a main floor MF of a clean room, while the excitationlaser source 300 is installed in a base floor BF located under the mainfloor MF. Each of the EUV radiation source 100 and the exposure device200 are placed over pedestal plates PP1 and PP2 via dampers DP1 and DP2,respectively. The EUV radiation source 100 and the exposure device 200are coupled to each other by a coupling mechanism, which may include afocusing unit.

The EUV lithography tool is designed to expose a resist layer to EUVlight (also interchangeably referred to herein as EUV radiation). Theresist layer is a material sensitive to the EUV light. The EUVlithography system employs the EUV radiation source 100 to generate EUVlight, such as EUV light having a wavelength ranging between about 1 nmand about 100 nm. In one particular example, the EUV radiation source100 generates an EUV light with a wavelength centered at about 13.5 nm.In the present embodiment, the EUV radiation source 100 utilizes amechanism of laser-produced plasma (LPP) to generate the EUV radiation.

The exposure device 200 includes various reflective optic components,such as convex/concave/flat mirrors, a mask holding mechanism includinga mask stage, and wafer holding mechanism. The EUV radiation EUVgenerated by the EUV radiation source 100 is guided by the reflectiveoptical components onto a mask secured on the mask stage. In someembodiments, the mask stage includes an electrostatic chuck (e-chuck) tosecure the mask.

FIG. 2 is a simplified schematic diagram of a detail of an extremeultraviolet lithography tool according to an embodiment of thedisclosure showing the exposure of photoresist coated substrate 210 witha patterned beam of EUV light. The exposure device 200 is an integratedcircuit lithography tool such as a stepper, scanner, step and scansystem, direct write system, device using a contact and/or proximitymask, etc., provided with one or more optics 205 a, 205 b, for example,to illuminate a patterning optic 205 c, such as a reticle, with a beamof EUV light, to produce a patterned beam, and one or more reductionprojection optics 205 d, 205 e, for projecting the patterned beam ontothe substrate 210. A mechanical assembly (not shown) may be provided forgenerating a controlled relative movement between the substrate 210 andpatterning optic 205 c. As further shown in FIG. 2, the EUVL toolincludes an EUV light source 100 including an EUV light radiator ZEemitting EUV light in a chamber 105 that is reflected by a collector 110along a path into the exposure device 200 to irradiate the substrate210.

As used herein, the term “optic” is meant to be broadly construed toinclude, and not necessarily be limited to, one or more components whichreflect and/or transmit and/or operate on incident light, and includes,but is not limited to, one or more lenses, windows, filters, wedges,prisms, grisms, gradings, transmission fibers, etalons, diffusers,homogenizers, detectors and other instrument components, apertures,axicons and mirrors including multi-layer mirrors, near-normal incidencemirrors, grazing incidence mirrors, specular reflectors, diffusereflectors and combinations thereof. Moreover, unless otherwisespecified, the term “optic”, as used herein, is directed to, but notlimited to, components which operate solely or to advantage within oneor more specific wavelength range(s) such as at the EUV output lightwavelength, the irradiation laser wavelength, a wavelength suitable formetrology or any other specific wavelength.

Because gas molecules absorb EUV light, the lithography system for theEUV lithography patterning is maintained in a vacuum or a low pressureenvironment to avoid EUV intensity loss. However, hydrocarbon-containinggases exist in a vacuum or a low pressure environment. Therefore, inreality, in the EUV lithography system, a presence of adventitiousgaseous organic compound 400 (interchangeably referred to ashydrocarbon-containing gas) is inevitably present in the exposure device200 and the chamber 105.

In the present disclosure, the terms mask, photomask, and reticle areused interchangeably. In the present embodiment, the patterning optic205 c is a reflective mask. In an embodiment, the reflective mask 205 cincludes a substrate with a suitable material, such as a low thermalexpansion material or fused quartz. In various examples, the materialincludes TiO₂ doped SiO₂, or other suitable materials with low thermalexpansion. The reflective mask 205 c includes multiple reflective layers(ML) deposited on the substrate. The ML includes a plurality of filmpairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer ofmolybdenum above or below a layer of silicon in each film pair).Alternatively, the ML may include molybdenum-beryllium (Mo/Be) filmpairs, or other suitable materials that are configured to highly reflectthe EUV light. The mask 205 c may further include a capping layer,having a top portion made of a metal element and at least one nonmetalelement, disposed on the ML for minimizing oxidation of the ML. The maskfurther includes an absorption layer (interchangeably referred to asabsorber layer), such as a tantalum boron nitride (TaBN) layer,deposited over the ML. The absorption layer is patterned to define alayer of an integrated circuit (IC). Alternatively, another reflectivelayer may be deposited over the ML and is patterned to define a layer ofan integrated circuit, thereby forming an EUV phase shift mask.

In various embodiments of the present disclosure, the photoresist coatedsubstrate 210 is a semiconductor wafer, such as a silicon wafer or othertype of wafer to be patterned.

The EUVL tool further includes other modules or is integrated with (orcoupled with) other modules in some embodiments.

As shown in FIG. 1, the EUV radiation source 100 includes a targetdroplet generator 115 and a LPP collector 110, enclosed by a chamber105. In various embodiments, the target droplet generator 115 includes areservoir to hold a source material and a nozzle 120 through whichtarget droplets DP of the source material are supplied into the chamber105.

In some embodiments, the target droplets DP are droplets of tin (Sn),lithium (Li), or an alloy of Sn and Li. In some embodiments, the targetdroplets DP each have a diameter in a range from about 10 microns (μm)to about 100 μm. For example, in an embodiment, the target droplets DPare tin droplets, having a diameter of about 10 μm to about 100 μm. Inother embodiments, the target droplets DP are tin droplets having adiameter of about 25 μm to about 50 μm. In some embodiments, the targetdroplets DP are supplied through the nozzle 120 at a rate in a rangefrom about 50 droplets per second (i.e., an ejection-frequency of about50 Hz) to about 50,000 droplets per second (i.e., an ejection-frequencyof about 50 kHz).

Referring back to FIG. 1, an excitation laser LR2 generated by theexcitation laser source 300 is a pulse laser. The laser pulses LR2 aregenerated by the excitation laser source 300. The excitation lasersource 300 may include a laser generator 310, laser guide optics 320 anda focusing apparatus 330. In some embodiments, the laser generator 310includes a carbon dioxide (CO₂) or a neodymium-doped yttrium aluminumgarnet (Nd:YAG) laser source with a wavelength in the infrared region ofthe electromagnetic spectrum. For example, the laser generator 310 has awavelength of about 9.4 μm or about 10.6 μm, in an embodiment. The laserlight LR1 generated by the laser generator 310 is guided by the laserguide optics 320 and focused into the excitation laser LR2 by thefocusing apparatus 330, and then introduced into the EUV radiationsource 100.

In some embodiments, the excitation laser LR2 includes a pre-heat laserand a main laser. In such embodiments, the pre-heat laser pulse(interchangeably referred to herein as the “pre-pulse”) is used to heat(or pre-heat) a given target droplet to create a low-density targetplume with multiple smaller droplets, which is subsequently heated (orreheated) by a pulse from the main laser, generating increased emissionof EUV light.

In various embodiments, the pre-heat laser pulses have a spot size about100 μm or less, and the main laser pulses have a spot size in a range ofabout 150 μm to about 300 μm. In some embodiments, the pre-heat laserand the main laser pulses have a pulse-duration in the range from about10 ns to about 50 ns, and a pulse-frequency in the range from about 1kHz to about 100 kHz. In various embodiments, the pre-heat laser and themain laser have an average power in the range from about 1 kilowatt (kW)to about 50 kW. The pulse-frequency of the excitation laser LR2 ismatched with (e.g., synchronized with) the ejection-frequency of thetarget droplets DP in an embodiment.

The excitation laser LR2 is directed through windows (or lenses) intothe zone of excitation ZE. The windows are made of a suitable materialsubstantially transparent to the laser beams. The generation of thepulse lasers is synchronized with the ejection of the target droplets DPthrough the nozzle 120. As the target droplets move through theexcitation zone, the pre-pulses heat the target droplets and transformthem into low-density target plumes. A delay between the pre-pulse andthe main pulse is controlled to allow the target plume to form and toexpand to an optimal size and geometry. In various embodiments, thepre-pulse and the main pulse have the same pulse-duration and peakpower. When the main pulse heats the target plume, a high-temperatureplasma is generated. The plasma emits EUV radiation EUV, which iscollected by the collector mirror 110. The collector 110 furtherreflects and focuses the EUV radiation for the lithography exposingprocesses performed through the exposure device 200. The droplet catcher125 is used for catching excessive target droplets. For example, sometarget droplets may be purposely missed by the laser pulses.

In some embodiments, the collector 110 is designed with a proper coatingmaterial and shape to function as a mirror for EUV collection,reflection, and focusing. In some embodiments, the collector 110 isdesigned to have an ellipsoidal geometry. In some embodiments, thecoating material of the collector 110 is similar to the reflectivemultilayer of the EUV mask. In some examples, the coating material ofthe collector 110 includes a ML (such as a plurality of Mo/Si filmpairs) and may further include a capping layer (such as Ru) coated onthe ML to substantially reflect the EUV light. In some embodiments, thecollector 110 may further include a grating structure designed toeffectively scatter the laser beam directed onto the collector 110. Forexample, a silicon nitride layer is coated on the collector 110 and ispatterned to have a grating pattern.

In such an EUV radiation source, the plasma caused by the laserapplication creates dissociation of gaseous organic compound 400. Forexample, during the EUV lithography, the gaseous organic compound 400tends to be negatively charged. The negatively charged gaseous organiccompound 400 would cross-link undesirably with the Ru material in thecapping layer in the reflective mask 205 c, which in turn leads tocarbon unwantedly deposited on the capping layer, thus degrading thecritical dimension (CD) of the resulting pattern formed on thephotoresist-coated substrate 21. Embodiments of the present disclosureprovide an improved composition for the capping layer so as to preventthe dissociated gaseous organic compound from cross-linking with the Rumaterial in the capping layer.

FIGS. 3A, 3B, 3C and 3D are cross-sectional views of various stages of aprocess for forming an extreme ultraviolet (EUV) mask 6 in accordancewith some embodiments. It is understood that additional operations canbe provided before, during, and after processes shown by FIGS. 3A, 3B,3C and 3D and some of the operations described below can be replaced oreliminated, for additional embodiments of the method. The order of theoperations/processes may be interchangeable.

Reference is made to FIG. 3A. A multilayer Mo/Si stack 15 of multiplealternating layers of silicon and molybdenum and a capping layer 20 areformed over a substrate 10 in sequence.

The substrate 10 is formed of a low thermal expansion material in someembodiments. In some embodiments, the substrate 10 is a low thermalexpansion glass or quartz, such as fused silica or fused quartz. In someembodiments, the low thermal expansion glass substrate transmits lightat visible wavelengths, a portion of the infrared wavelengths near thevisible spectrum (near-infrared), and a portion of the ultravioletwavelengths. In some embodiments, the low thermal expansion glasssubstrate absorbs extreme ultraviolet wavelengths and deep ultravioletwavelengths near the extreme ultraviolet.

In some embodiments, the Mo/Si multilayer stack 15 includes from about30 alternating layers each of silicon and molybdenum to about 60alternating layers each of silicon and molybdenum. In some embodiments,the silicon and molybdenum layers are formed by chemical vapordeposition (CVD), plasma-enhanced CVD (PECVD), atomic layer deposition(ALD), physical vapor deposition (PVD) (sputtering), or any othersuitable film forming method. In some embodiments, the layers of siliconand molybdenum are about the same thickness. In other embodiments, thelayers of silicon and molybdenum are different thicknesses.

The capping layer 20 is disposed over the multilayer Mo/Si stack 15 toprevent oxidation of the multilayer Mo/Si stack 15 during a maskpatterning process and an absorber layer repairing process. In addition,the capping layer 20 acts as an etch stop in an absorber layerpatterning process. In some embodiments, the capping layer 20 is formedby chemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), atomic layer deposition (ALD), physical vapordeposition (PVD), or any other suitable film forming method. The cappinglayer 20 has a first composition. In some embodiments, the firstcomposition includes one pure metal element, which has metallic bonds,such as a transition metal. For example, the first composition includesruthenium (Ru).

Reference is made to FIG. 3B. A doping process 500 is performed on thecapping layer 20 to dope a top portion of the capping layer 20 with adopant to form a doped top portion 20A. A bottom portion 20B of thecapping layer 20 may remain un-doped or has a lower dopant concentrationthan the top portion 20A. The doping process 500 may include ionimplantation and/or other suitable processes. In some embodiments, thedopant includes at least one nonmetal element that has highelectronegativity difference from ruthenium. For example, the dopant(interchangeably referred to as impurity) is a halogen element (e.g.,fluorine, chlorine or the like), a pentavalent element (nitrogen or thelike), or a hexavalent element (oxygen or the like). Precursors of thefluorine element may include fluorine-containing gas. By way of exampleand not limitation, the fluorine-containing gas may be GeF₄, NF₃, CF₄,C₂F₆, F₂, the like, or mixtures thereof. Precursors of the chlorineelement may include chlorine-containing gas. By way of example and notlimitation, the chlorine-containing gas may include Cl₂, CHCl₃, CCl₄,BCl₃, the like, or mixtures thereof. Precursors of the pentavalentelement (nitrogen or the like) may include nitrogen-containing gas. Byway of example and not limitation, the nitrogen-containing gas mayinclude ammonia (NH₃), dimethyl amine (N(CH₃)₂), dimethyl amine(N(C₂H₅)₂), the like, or mixtures thereof. Precursors of the hexavalentelement (oxygen or the like) may include oxygen-containing gas. By wayof example and not limitation, the oxygen-containing gas includes H₂O,D₂O, O₃, O₂, the like, or mixtures thereof.

Once the doping process 500 is complete, the doped top portion 20A has asecond composition different from the first composition of thesubstantially un-doped bottom portion 20B. A molecular weight of thesecond composition is greater than a molecular weight of the firstcomposition. In some embodiments, the second composition includes themetal element and the doped impurity (e.g., halogen impurity,pentavalent impurity or hexavalent impurity). In particular, the secondcomposition and the first composition have different chemical bondingtypes. In some embodiments where the first composition includes atransition metal, since the transition metal has a tendency to acceptelectrons, the doped impurity may react with the transition metal toform a stable coordination complex. In some embodiments where the firstcomposition includes ruthenium, the second composition may include atleast one ruthenium complex, such as Ru_(x)O_(1-x), Ru_(x)N_(1-x),Ru_(x)A_(y)O_(1-x-y) (where A is a halogen atom), or the like. Stateddifferently, the second composition includes a ruthenium complex with aligand having a halogen element, a pentavalent element, a hexavalentelement or combinations thereof. The ruthenium forms chemical bonds(e.g., ionic bonds for halogen element) having high electronegativitydifference with the halogen element, pentavalent element or hexavalentelement, which in turn places ruthenium in a stable state with a valencenumber of 16 or 18. Since the halogen element, pentavalent element orhexavalent element may fill electron vacancy in ruthenium, the unwantedcross-link between the adventitious gaseous organic compound 400 in theEUV lithography system and the doped top portion 20A of the cappinglayer 20 may be prevented, which will be described in greater detailbelow.

Reference is made to FIG. 3C. An absorber layer 25 is disposed over thecapping layer 20. An anti-reflection layer 30 is disposed over theabsorber layer 25. Thus, an EUV photo mask blank 5 is formed. In someembodiments, the absorber layer 25 is a Ta-based material. In someembodiments, the absorber layer 25 is made of TaN and/or TaBN. In someembodiments, the absorber layer 25 is formed by chemical vapordeposition, plasma-enhanced chemical vapor deposition, atomic layerdeposition, physical vapor deposition, or any other suitable filmforming method. The anti-reflection layer 30 is formed of a materialincluding SiO₂, SiN, TaBO, TaO₅, Cr₂O₃, ITO (indium tin oxide), or anysuitable material, in some embodiments of the present disclosure. Theanti-reflection layer 30 reduces reflections of photolithographicradiation.

Reference is made to FIG. 3D. One or more circuit patterns 50 are formedon the EUV photo mask blank 5 (see FIG. 3C) by performing an etchingstep 600 to pattern the absorber layer 25 and the anti-reflection layer30. Thus, an EUV mask 6 is formed. The EUV mask 6 is a reflective mask,and the Mo/Si multilayer stack 15 reflects the EUV light, while theabsorber layer 25 absorbs the EUV light. During the patterning, theabsorber layer 25 and the anti-reflection layer 30 are partiallyremoved. For example, the absorber layer 25 is etched to expose thedoped top portion 20A of the capping layer 20. In addition, a blackborder area 60 surrounding a circuit pattern region and penetrating tothe substrate 10 is formed. The circuit patterns 50 are formed by usingone or more lithography (e.g., electron beam lithography) and etchingoperations. In some examples, the area in which no circuit pattern isformed is covered by an absorber layer 25 so that the EUV light is notreflected.

FIGS. 4A and 4B illustrates how cross-link occurs on the Ru cappinglayer during the EUV lithography process, if the capping layer is freeof the halogen element, the pentavalent element or the hexavalentelement. FIG. 4A is a cross-sectional view of the EUV mask 6 underexposure of the EUV radiation in accordance with some embodiments. FIG.4B is a diagram illustrating a mechanism S100 of hydrocarbon formed froma gaseous organic compound deposited on the doped top portion 20A of thecapping layer 20 of the EUV mask 6 in FIG. 4A. Reference is made toFIGS. 4A and 4B. For the sake of clarity, steps of the mechanism S100are labeled as S102, S104, S106, and S106. As illustrated, the EUVradiation is incident on the EUV mask 6. In step S102, the EUV radiationinduces a dissociation of the gaseous organic compound 400 such ashydrocarbons to form hydrocarbon fragments 402. The hydrocarbonfragments 402 are not a cross-linked structure. Therefore, thehydrocarbon fragments 402 are dissociable to EUV radiation and amajority of the hydrocarbon fragments 402 does not tend to be depositedon the surface of the doped top portion 20A. In some embodiments, aminority of the hydrocarbon fragment 402 may be deposited on the surfaceof the doped top portion 20A. For example, in step S104, the hydrocarbonfragments may absorb on the surface of the doped top portion 20A of thecapping layer 20. Then, in step S106, the hydrocarbon fragments 402diffuse along the surface of the doped top portion 20A. Undesirablecross-link structures 404 formed of cross-link between the hydrocarbonfragments 402 and the doped top portion 20A of the capping layer (stepS108) caused by secondary electrons SE with an energy of less than about20 eV induced by the EUV irradiation can be reduced, as compared withthe case where the top portion of the ruthenium capping layer is free ofthe halogen element, pentavalent element or hexavalent element. This isbecause the electron vacancy of ruthenium in the doped top portion 20Aof the capping layer 20 has already been filled by the halogen element,pentavalent element or hexavalent element.

FIGS. 5A, 5B, and 5C are cross-sectional views of various stages of aprocess for forming an extreme ultraviolet (EUV) mask in accordance withsome embodiments. Reference is made to FIG. 5A. FIG. 5A shows anotherEUV photo mask blank 5 a similar to the EUV photo mask blank 5, exceptthat the capping layer 20 a remains un-doped prior to forming theoverlying absorber layer 25, instead of doped. In greater detail, theEUV photo mask blank 5 a includes a substrate 10, a Mo/Si multilayerstack 15, a capping layer 20 a, an absorber layer 25 and ananti-reflection layer 30. As shown in FIG. 5A, the Mo/Si multilayerstack 15, the capping layer 20 a, the absorber layer 25 and theanti-reflection layer 30 are formed over the substrate 10 in sequenceusing suitable methods, as discussed previously with respect to FIGS. 3Aand 3C.

Reference is made to FIG. 5B. One or more circuit patterns 50 are formedon the EUV photo mask blank 5 a by performing an etching step 600 a topattern the absorber layer 25 and the anti-reflection layer 30. Duringthe etching step 600 a, the absorber layer 25 and the anti-reflectionlayer 30 are partially removed. Therefore, a top portion of the cappinglayer 20 a is partially exposed. In addition, a black border area 60surrounding a circuit pattern region and penetrating to the substrate isformed. The circuit patterns 50 are formed by using one or morelithography (e.g., electron beam lithography) and etching operations. Insome examples, the area in which no circuit pattern is formed is coveredby an absorber layer 25 so that the EUV light is not reflected.

Reference is made to FIG. 5C. In particular, in some embodiments, adoping process 500 a is performed on the top portion of the cappinglayer 20 a exposed by the circuit patterns 50 with a dopant to form aplurality of doped top portions 20 aA after performing the etching step600 a. Thus, an EUV mask 6 a is formed. The bottom portions 20 aB of thecapping layer 20 a respectively directly under the doped top portions 20aA remain substantially un-doped or have a lower doped impurityconcentration than the doped top portions 20 aA, and a remaining portionof the capping layer 20 a covered by the absorber layer 25 remainsubstantially un-doped during the doping process 500 a. The dopingprocess 500 a may include ion implantation or the like. In someembodiments, the dopant includes at least one nonmetal element that hashigh electronegativity difference from ruthenium. For example, thedopant (interchangeably referred to as impurity) is a halogen element(e.g., fluorine, chlorine or the like), a pentavalent element (nitrogenor the like), or a hexavalent element (oxygen or the like). In someembodiments, the anti-reflection layer 30 and the underlying absorberlayer 25 act as an implantation mask during the doping process 500 a,such that the doped top portions 20 aA have the same pattern as thecircuit patterns 50 when viewed from above. Because the anti-reflectionlayer 30 is exposed during the doping process 500 a, a top portion ofthe anti-reflection layer 30 may be unintentionally doped with thehalogen element, pentavalent element or hexavalent element. In suchscenarios, the top portion of the anti-reflection layer 30 has a halogenelement, a pentavalent element or a hexavalent element same as that inthe doped top portions 20 aA of the capping layer 20 a.

Once the doping process 500 a is complete, the doped top portion 20 aAhas a second composition different from the first composition of thesubstantially un-doped bottom portion 20 aB and of the portions of thecapping layer 20 a covered by the absorber layer 25. A molecular weightof the second composition is greater than a molecular weight of thefirst composition. The second composition includes the metal element andthe doped impurity (e.g., halogen element, pentavalent element orhexavalent element). In particular, the second composition and the firstcomposition have different chemical bonding types. In some embodimentswhere the first composition includes a transition metal, since thetransition metal has a tendency to accept electrons, the doped impuritymay react with the transition metal to form a stable coordinationcomplex. In some embodiments where the first composition includesruthenium, the second composition may include at least one rutheniumcomplex, such as Ru_(x)O_(1-x), Ru_(x)A_(y)O_(1-x-y) (where A is ahalogen atom), or the like. The ruthenium forms chemical bonds (e.g.,ionic bonds for halogen element) having high electronegativitydifference with the halogen element, pentavalent element or hexavalentelement, such that the ruthenium is in a stable state with a valencenumber of 16 or 18. Since the halogen element, pentavalent element orhexavalent element may fill electron vacancy in ruthenium, the unwantedcross-link between the adventitious gaseous organic compound in the EUVlithography system and the doped top portion 20 aA of the capping layer20 a may be prevented.

FIG. 6 is a cross-sectional view of various stages of a process forforming an extreme ultraviolet (EUV) mask 6 a′ in accordance with someembodiments. Reference is made to FIG. 6. In some other embodiments, thetop portion of the capping layer 20 a′ exposed by the circuit patterns50 is in-situ doped by adding the dopant, such as nitrogen, halogenand/or oxygen, during the etching process 600 a′ performed on the EUVphoto mask blank 5 a (see FIG. 5B) to form the circuit patterns 50. Inother words, the step of the etching process 600 a′ is performedsimultaneously with in-situ doping the halogen impurity, pentavalentimpurity or hexavalent impurity into the exposed top portion of thecapping layer 20 a′. Thus, an EUV mask 6 a′ is formed with circuitpatterns 50 as well as the doped capping layer 20 a′. By way of exampleand not limitation, the etching process 600 a′ may be performed by usingan oxygen-containing gas, a fluorine-containing gas (e.g., CF₄, SF₆,CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containing gas (e.g., Cl₂, CHCl₃,CCl₄, and/or BCl₃), a bromine-containing gas (e.g., HBr and/or CHBR₃),an iodine-containing gas, other suitable gases and/or plasmas, and/orcombinations thereof. The in-situ doping process during the etchingprocess 600 a′ may be performed by introducing precursors of a halogenelement (e.g., fluorine, chlorine or the like), a pentavalent element(nitrogen or the like), or a hexavalent element (oxygen or the like).Precursors of the fluorine element may include fluorine-containing gas,such as GeF₄, NF₃, CF₄, C₂F₆, F₂, the like, or mixtures thereof.Precursors of the chlorine element may include chlorine-containing gas,such as Cl₂, CHCl₃, CCl₄, BCl₃, the like, or mixtures thereof.Precursors of the pentavalent element (nitrogen or the like) mayinclude, but is not limited to, ammonia (NH₃), dimethyl amine (N(CH₃)₂),dimethyl amine (N(C₂H₅)₂), the like, or mixtures thereof. Precursors ofthe hexavalent element (oxygen or the like) may include, but is notlimited to, H₂O, D₂O, O₃, O₂, the like, or mixtures thereof.

The bottom portions 20 aB′ of the capping layer 20 a′ respectivelydirectly under the doped top portions 20 aA′ remain substantiallyun-doped or have a lower doped impurity concentration than the doped topportions 20 aA′. Portions of the capping layer 20 a′ directly under theabsorber layer 30 remain substantially un-doped as well. In someembodiments, the anti-reflection layer 30 and the underlying absorberlayer 25 act as an implantation mask during the in-situ doping process,such that the doped top portions 20 aA′ have the same pattern as thecircuit patterns 50 when viewed from above. In some embodiments, a topportion of the anti-reflection layer 30 may be unintentionally dopedwith the halogen impurity, pentavalent impurity or hexavalent impurity.In such scenarios, the top portion of the anti-reflection layer 30 has ahalogen element, a pentavalent element or a hexavalent element same asthat in the doped top portions 20 aA′ of the capping layer 20 a′.

FIG. 7A shows a flowchart illustrating a method S200 of manufacturing anEUV mask according to some embodiments of the present disclosure. It isunderstood that in the sequential manufacturing process, one or moreadditional operations can be provided before, during, and after thestages shown in FIG. 7A and some of the operations described below canbe replaced or eliminated for additional embodiments of the method. Theorder of the operations/processes may be interchangeable. At step S202,a multilayer Mo/Si stack of multiple alternating layers of silicon andmolybdenum and a capping layer are formed in sequence on a substrate. Atstep S204, a doping process is performed on the capping layer to dope atop portion of the capping layer with the halogen impurity, pentavalentimpurity or hexavalent impurity to form a doped top portion. At stepS206, an absorber layer formed and an anti-reflection layer are formedon the doped top portion of the capping layer to form an EUV photo maskblank. At step S208, one or more circuit patterns are formed on the EUVphoto mask blank by patterning the anti-reflection layer and theabsorber layer to expose the doped top portion of the capping layer.

FIG. 7B shows a flowchart illustrating a method S300 of manufacturing anEUV mask according to some embodiments of the present disclosure. It isunderstood that in the sequential manufacturing process, one or moreadditional operations can be provided before, during, and after thestages shown in FIG. 7B and some of the operations described below canbe replaced or eliminated for additional embodiments of the method. Theorder of the operations/processes may be interchangeable. At step S302,a Mo/Si multilayer stack, a capping layer, an absorber layer and ananti-reflection layer are formed on a substrate in sequence to form anEUV photo mask blank. At step S304, one or more circuit patterns areformed on the EUV photo mask blank by patterning the anti-reflectionlayer and the absorber layer. At step S306, a doping process isperformed to dope the top portion of the capping layer exposed by thecircuit patterns with the halogen impurity, pentavalent impurity orhexavalent impurity.

FIG. 7C shows a flowchart illustrating a method S400 of manufacturing anEUV mask for a semiconductor manufacturing operation according to anembodiment of the present disclosure. At step S402, a Mo/Si multilayerstack, a capping layer, an absorber layer and an anti-reflection layerare formed on a substrate in sequence to form an EUV photo mask blank.At step S404, one or more circuit patterns 50 are formed on the EUVphoto mask blank by patterning the anti-reflection layer and theabsorber layer, and the patterning step is performed simultaneously within-situ doping the halogen impurity, pentavalent impurity or hexavalentimpurity into the capping layer.

FIG. 8 shows a flowchart illustrating a method S500 of extremeultraviolet lithography (EUVL) according to an embodiment of the presentdisclosure. In some embodiments, the method S500 is performed by thecomputer system 900 of FIGS. 9A and 9B. The method S500 includes anoperation S502 of generating plasma in an EUV lithography systemincluding a gaseous organic compound. The EUV lithography system forms aprojection beam of EUV radiation using EUV radiation emitted from aradiation source. In operation S504, an EUV mask is exposed to theprojection beam of EUV radiation. The gaseous organic compound is notcross-linked with the EUV mask. In operation S506, a photoresist coatedsemiconductor wafer is exposed to the projection beam of EUV radiationreflecting off the EUV mask. Operation S502 is triggered by turning onthe laser source 300 and the droplet generator 115 as illustrated inFIG. 1, and the operations S504 and S506 occur naturally once theoperation S502 is triggered, as long as the optics 205 a-205 e aresuitably oriented to direct the EUV projection beam.

FIGS. 9A and 9B show a photo mask data generating apparatus according toan embodiment of the present disclosure. FIG. 9A is a schematic view ofa computer system that executes the photo mask data generating processaccording to one or more embodiments as described above. All of or apart of the process, method and/or operations of the foregoingembodiments can be realized using computer hardware and computerprograms executed thereon. In FIG. 9A, a computer system 900 is providedwith a computer 901 including an optical disk read only memory (e.g.,CD-ROM or DVD-ROM) drive 905 and a magnetic disk drive 906, a keyboard902, a mouse 903, and a monitor 904.

FIG. 9B is a diagram showing an internal configuration of the computersystem 900. In FIG. 9B, the computer 901 is provided with, in additionto the optical disk drive 905 and the magnetic disk drive 906, one ormore processors 911, such as a micro processing unit (MPU), a ROM 912 inwhich a program such as a boot up program is stored, a random accessmemory (RAM) 913 that is connected to the MPU 911 and in which a commandof an application program is temporarily stored and a temporary storagearea is provided, a hard disk 914 in which an application program, asystem program, and data are stored, and a bus 915 that connects the MPU911, the ROM 912, and the like. Note that the computer 901 may include anetwork card (not shown) for providing a connection to a LAN.

The program for causing the computer system 900 to execute the functionsof the photo mask data generating apparatus in the foregoing embodimentsmay be stored in an optical disk 921 or a magnetic disk 922, which areinserted into the optical disk drive 905 or the magnetic disk drive 906,and transmitted to the hard disk 914. Alternatively, the program may betransmitted via a network (not shown) to the computer 901 and stored inthe hard disk 914. At the time of execution, the program is loaded intothe RAM 913. The program may be loaded from the optical disk 921 or themagnetic disk 922, or directly from a network.

The program does not necessarily have to include, for example, anoperating system (OS) or a third party program to cause the computer 901to execute the functions of the photo mask data generating apparatus inthe foregoing embodiments. The program may only include a commandportion to call an appropriate function (module) in a controlled modeand obtain desired results.

In the programs, the functions realized by the programs do not includefunctions that can be realized only by hardware in some embodiments. Forexample, functions that can be realized only by hardware, such as anetwork interface, in an acquiring unit that acquires information or anoutput unit that outputs information are not included in the functionsrealized by the above-described programs in some embodiments.Furthermore, a computer that executes the programs may be a singlecomputer or may be multiple computers.

Further, the entirety of or a part of the programs to realize thefunctions of the photo mask data generating apparatus is a part ofanother program used for photo mask fabrication processes in someembodiments. In addition, the entirety of or a part of the programs torealize the functions of the photo mask data generating apparatus isrealized by a ROM made of, for example, a semiconductor device in someembodiments.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. One advantage is that unwanted carbondeposition upon the ruthenium capping layer in the EUV mask can bealleviated by the doping the ruthenium capping layer with a halogenelement, a pentavalent element, a hexavalent element or combinationsthereof, which in turn will address the CD degradation issue in theresulting pattern formed using the EUV lithography technique. Anotheradvantage is that the bottom portion of the ruthenium capping layerremains substantially un-doped (i.e., remaining substantially pureruthenium), so that the capping layer can still protect the underlyingMo/Si ML structure from unwanted oxidation.

In some embodiments, a method of forming an extreme ultraviolet (EUV)mask includes forming a multilayer Mo/Si stack comprising alternatingstacked Mo and Si layers over a mask substrate; forming a rutheniumcapping layer over the multilayer Mo/Si stack; doping the rutheniumcapping layer with a halogen element, a pentavalent element, ahexavalent element or combinations thereof; forming an absorber layerover the ruthenium capping layer; and etching the absorber layer to forma pattern in the absorber layer.

In some embodiments, an extreme ultraviolet lithography (EUVL) methodincludes turning on a droplet generator to eject a metal droplet towarda zone of excitation in front of a collector; turning on a laser sourceto emit a laser toward the zone of excitation, such that the metaldroplet is heated by the laser to generate EUV radiation; guiding theEUV radiation, by using one or more first optics, toward a reflectivemask in an exposure device, the reflective mask comprising a cappinglayer having a ruthenium complex with a ligand, the ligand having ahalogen element, a pentavalent element, a hexavalent element orcombinations thereof; and guiding the EUV radiation, by using one ormore second optics, reflected from the reflective mask toward aphotoresist coated substrate in the exposure device.

In some embodiments, an extreme ultraviolet (EUV) mask includes amultilayer Mo/Si stack, a capping layer, and a patterned absorber layer.The multilayer Mo/Si stack includes alternating stacked Mo and Si layersdisposed over a mask substrate. The capping layer is on the multilayerMo/Si stack. A top portion of the capping layer has a first compositiondifferent from a second composition of a bottom portion of the cappinglayer under the top portion of the capping layer. A patterned absorberlayer is on the capping layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An extreme ultraviolet lithography (EUVL) method,comprising: turning on a droplet generator to eject a metal droplettoward a zone of excitation in front of a collector; turning on a lasersource to emit a laser toward the zone of excitation, such that themetal droplet is heated by the laser to generate EUV radiation; guidingthe EUV radiation, by using one or more first optics, toward areflective mask in an exposure device, the reflective mask comprising acapping layer having a ruthenium complex with a ligand, the ligandhaving a halogen element, a pentavalent element, a hexavalent element orcombinations thereof; and guiding the EUV radiation, by using one ormore second optics, reflected from the reflective mask toward aphotoresist coated substrate in the exposure device.
 2. The method ofclaim 1, wherein the capping layer of the reflective mask is notcross-linked with a hydrocarbon-containing gas in the exposure deviceduring generating the EUV radiation.
 3. The method of claim 2, whereinthe hydrocarbon-containing gas further exists in a chamber in which thecollector is located.
 4. The method of claim 2, wherein thehydrocarbon-containing gas is dissociated by the EUV radiation.
 5. Themethod of claim 1, wherein a bottom portion of the capping layer of thereflective mask is free of the ruthenium complex.
 6. The method of claim1, wherein the reflective mask further comprises a multilayer Mo/Sistack in contact with a portion of the capping layer that is free of theruthenium complex.
 7. The method of claim 1, wherein the reflective maskfurther comprises an anti-reflection layer, and a top portion of theanti-reflection layer is doped with the halogen element, the pentavalentelement or the hexavalent element.
 8. An extreme ultraviolet lithography(EUVL) method, comprising: turning on a droplet generator to eject ametal droplet toward a zone of excitation in front of a collector;turning on a laser source to emit a laser toward the zone of excitation,such that the metal droplet is heated by the laser to generate EUVradiation; guiding the EUV radiation, by using one or more first optics,toward a reflective mask in an exposure device, the reflective maskcomprising: a multilayer Mo/Si stack comprising alternating Mo and Silayers over a mask substrate; a capping layer on the multilayer Mo/Sistack, wherein the capping layer has a doped top portion and an un-dopedbottom portion; and a patterned layer on the capping layer; and guidingthe EUV radiation, by using one or more second optics, reflected fromthe reflective mask toward a photoresist coated substrate in theexposure device.
 9. The method of claim 8, wherein the doped top portionhas dopants including at least one nonmetal element that haselectronegativity difference from ruthenium.
 10. The method of claim 8,wherein the doped top portion has dopants including a halogen element, apentavalent element, or a hexavalent element.
 11. The method of claim 8,wherein the capping layer further has an un-doped top portion in contactwith a lateral surface of the doped top portion.
 12. The method of claim11, wherein the patterned layer covers the un-doped top portion withoutcovering the doped top portion.
 13. The method of claim 8, wherein thedoped top portion of the capping layer of the reflective mask is notcross-linked with a hydrocarbon-containing gas in the exposure deviceduring generating the EUV radiation.
 14. The method of claim 8, whereinthe reflective mask further comprises an anti-reflection layer, and theanti-reflection layer and the doped top region have the same dopants.15. An extreme ultraviolet lithography (EUVL) method, comprising:turning on a droplet generator to eject a metal droplet toward a zone ofexcitation in front of a collector; turning on a laser source to emit alaser toward the zone of excitation, such that the metal droplet isheated by the laser to generate EUV radiation; guiding the EUVradiation, by using one or more first optics, toward a reflective maskin an exposure device, the reflective mask comprising: a multilayerMo/Si stack comprising alternating Mo and Si layers over a masksubstrate; a capping layer on the multilayer Mo/Si stack; a patternedlayer on the capping layer, wherein the capping layer has a first topregion exposed by the patterned layer and a second top region covered bythe patterned layer, the first top region has a first composition havinga first chemical bonding type, the second top region has a secondcomposition having a second chemical bonding type different from thefirst chemical bonding type; and guiding the EUV radiation, by using oneor more second optics, reflected from the reflective mask toward aphotoresist coated substrate in the exposure device.
 16. The method ofclaim 15, wherein the first composition includes ruthenium, and thesecond composition includes at least one ruthenium complex.
 17. Themethod of claim 16, wherein the at least one ruthenium complex includesRu_(x)O_(1-x), Ru_(x)N_(1-x), Ru_(x)A_(y)O_(1-x-y), and A is a halogenatom.
 18. The method of claim 15, wherein a molecular weight of thesecond composition is greater than a molecular weight of the firstcomposition.
 19. The method of claim 15, wherein the capping layerfurther comprises a bottom region directly under the first top regionbeing substantially un-doped.
 20. The method of claim 15, wherein thecapping layer further comprises a bottom region directly under the firsttop region having a doped impurity concentration than a doped impurityconcentration of the first top region.